1. Field of the Invention
The present invention relates to a method for recording information into a rewritable thermal label of the non-contact type. More particularly, the present invention relates to a method for recording information into a rewritable thermal label of the non-contact type which decreases damages to the recording face of a recording medium after repeated recording and erasure of information in accordance with the non-contact method and enables the recording medium to be used repeatedly 1,000 times or more.
2. Description of Related Art
As the label for control of articles such as labels attached to plastic containers used for transporting foods, labels used for control of electronic parts and labels attached to cardboard boxes for physical distribution management, currently, labels having a heat-sensitive recording material are mainly used. In the heat-sensitive recording material, a heat-sensitive recording layer containing an electron-donating dye precursor which is, in general, colorless or colored slightly and an electron-accepting color developing agent as the main components is formed on a support. When the heat-sensitive recording material is heated by a heated head or a heated pen, the dye precursor and the color developing agent react instantaneously with each other, and a recorded image is obtained. As the heat sensitive recording material, rewritable labels which allows formation of an image, erasure of the formed image and rewriting of another image are increasingly used recently. When the label attached to an adherend is treated for rewriting without detaching the label from the adherend, it is necessary that the recorded images be erased while the label remains attached to the adherend and, thereafter, the label attached to the adherend be passed through an ordinary printer for rewriting of other images. For this purpose, it is necessary that the erasure and the writing be performed in accordance with a method performed without contacting the label.
For the repeated use of a label, in recent years, reversible heat sensitive recording materials which allow recording and erasure of images have been developed. Examples of such materials include (1) a reversible heat-sensitive recording material having a heat-sensitive layer which is formed on a substrate and contains a resin and an organic low molecular weight substance showing reversible changes in transparency depending on the temperature and (2) a reversible heat-sensitive recording material having a heat-sensitive color development layer which is formed on a substrate and contains a dye precursor and a reversible color developing agent.
However, damages are accumulated on the recording face of the recording medium after the repeated use in the case of the conventional rewritable thermal labels of the non-contact type. This causes a drawback in that the number of repeating in the use decreases due to the damages on the recording face. A further drawback arises for recording an image formed by a cluster of lines such as a solid image in that, when lines close to each other are recorded by the continuous scanning with a laser light, portions of the image recorded before are erased and a clear image is not obtained.
Specifically, in the conventional method of scanning with the laser light, a scanner along the X-axis and a scanner along the Y-axis are driven for each of many lines constituting a character or a figure based on the data of the coordinates of the locus, and this causes the following problems. Since the scanner along the X-axis and the scanner along the Y-axis are stopped at the beginning of the drawing (the starting point) and at the end of the drawing (the end point) of a line, the scanning mirrors along each of the axes are accelerated or decelerated at portions in the vicinity of the starting point and the end point. Since the laser beam is applied at the constant output during the period of the acceleration and the deceleration, the laser energy is applied in a greater amount at portions in the vicinity of the starting point and the end point than the amount at other portions, and degradation of the substrate takes place more markedly in the excessively irradiated portions. As another problem, when a character is drawn by connecting lines, degradation of the substrate takes place in the overlapped portion due to the repeated irradiation with the laser beam since a line drawn before is irradiated again with the laser beam. As still another problem, when an cluster of lines such as a bar code is drawn, the line of the bar code drawn before is erased or has a decreased concentration due to the drawing of the adjacent subsequent line depending on the relation between the time interval between the drawings of the adjacent lines and the temperature of the substrate caused by the irradiation with the laser beam. The scanner in the above descriptions means scanning mirrors.
References related to the above descriptions are as follows:    [Patent Reference 1] Japanese Patent Application Laid-Open No. 2003-118238.    [Patent Reference 2] Japanese Patent Application Laid-Open No. 2002-215038.    [Patent Reference 3] Japanese Patent Application Laid-Open No. 2003-320694.    [Patent Reference 4] Japanese Patent Application Laid-Open No. 2003-320695.    [Patent Reference 5] Japanese Patent Application Laid-Open No. 2004-90026.    [Patent Reference 6] Japanese Patent Application Laid-Open No. 2004-94510.